The invention relates to a propulsion system, such as a jet engine, for equipping an aircraft.
More specifically, the invention relates to a propulsion system comprising a centre or core engine, a pod placed around the engine in accordance with a common longitudinal axis, as well as a support strut or pylon by which the engine is connected to a structural element of the aircraft. This structural element can either be a wing element when the propulsion system is installed beneath the wing, or a rear element of the fuselage, when the propulsion system is installed laterally at the rear of the fuselage.
The invention is applicable to any propulsion system of this type, in which access to the engine equipments takes place by opening two cowls, having a C-shaped cross-section, which form an integral part of the pod and are articulated directly or indirectly to the strut supporting the engine.
As is diagrammatically illustrated in FIG. 1, in an aircraft propulsion system such as a turbofan engine, maintenance generally takes place by means of two pivoting cowls 1 forming an integral part of the pod 2. These cowls 1 are intercalated between an air intake structure 3, forming the front of the pod 2 in the air flow direction, and a rear part 4 of the pod, in which in general thrust reversers are located. The cowls 1 are articulated to the strut 5 either directly, or by means of fixed parts belonging to the pod 2.
The strut 5 is generally a beam for connecting the centre engine 6 to an aircraft wing element. The cowls 1 are then articulated to the strut by their upper edges.
In certain, rarer cases, the strut 5 is a lateral beam for connecting the centre engine 6 to the rear of the aircraft fuselage. The cowls 1 are then articulated to the strut by one of their lateral edges.
The opening of these cowls 1 makes it possible to ensure the maintenance of equipments of the engine 6. When closed, the cowls 1 ensure the continuity of the external aerodynamic shapes of the pod 2.
The cowls 1 are closed by not shown locking means, which connect the connecting edges of the cowls, opposite to those by which they are articulated to the strut 5. Thus, these locking means connect the lower edges of the cowls 1, when the propulsion system is placed beneath the wing of an aircraft.
In practice, the locking means are generally constituted by several hooked locks distributed along the connecting edges. Each lock comprises a hook installed on one of the cowls 1 and a fork carried by the other cowl 1. The hooks are installed on one of the cowls in a pivoting manner, so as to cover the facing forks, when the locks are in the locked state. In this locked state, the locks exert a tension between the two cowls. This tension, which is applied in a circumferential direction with respect to the longitudinal axis of the propulsion system is known as the xe2x80x9cbelt tensionxe2x80x9d.
When the cowls are in the closed position, their front and rear edges surround two circular bearing surfaces of limited length and large diameter. One 7 of these bearing surfaces is formed at the rear of the air intake structure 3 of the pod 2. The second bearing surface 8 is formed at the front of the rear part 4 of the pod.
Theoretically, the belt stress exerted by the locks on the cowls should constantly maintain the latter in bearing action over the entire periphery of the bearing surfaces 7, 8, by applying thereto a circumferential load.
In practice and as illustrated by FIGS. 2 and 3, the application of the circumferential load is reduced or even prevented by the bending of the engine 6 and the air intake structure 3 under their own weight, when the aircraft is on the ground.
In order to avoid their disassembly on removing the engine 6, the cowls 1 are articulated to the strut 5 and not directly to the engine. Therefore the cowls 1 are independent of small amplitude movements of the engine 6. Due to the fact that the different structures forming the propulsion system have a certain flexibility, which tends to increase over the years, all these structures bow under their own weight when the aircraft is on the ground. As is diagrammatically illustrated in FIGS. 2 and 3, the front of the engine 6 and the air intake structure 3 fixed to the latter then occupy a low position with respect to the cowls 1. The circumferential bearing area between the air intake structure 3 and the front edges of the cowls is then located in the lower part of the propulsion system. There is consequently a difference or variation J1 (FIG. 3) between the upper edge of each of the cowls 1 and the external envelope of the air intake structure 3.
When the aircraft is flying, the engine 6 and the air intake structure 3 are again in a higher position under the effect of thrust and aerodynamic forces, as illustrated in FIG. 4. The circular bearing surface 7 formed on the air intake structure 3 then abuts on the upper part of the front edges of the cowls 1. In view of the fact that the latter are not directly connected either to the engine 6, or to the air intake structure 3, they are unable to follow this vertical, upward displacement of the air intake structure. Thus, in the lower part, there is a mismatching between the front edges of the cowls 1 and the circular bearing surface 7 formed on the air intake structure 3. This mismatching, which has been deliberately exaggerated in FIG. 4, is designated in the latter by the reference J2.
When the mismatching J2 is limited, it gives rise to a significant erosion of the front edges of the cowls 1, in the upper part of the latter when the aircraft is on the ground and in their lower part when the aircraft is flying. In the case of a more pronounced mismatching J2, in flight there is an intake of air disturbing the ventilation of the internal area of the cowls 1.
Finally, in the case of a considerable mismatching J2, of e.g. approximately 1 cm, the intake of air has the effect of pressurizing the inner faces of the cowls 1, which can lead to the loss thereof, if one of the locks is poorly set or locked.
Moreover, the integrity of the locking function requires that the two parts of each lock, i.e. the hook connected to one of the cowls 1 and the fork connected to the other cowl, are permanently in contact. If this condition is not satisfied, there is a danger of the hook becoming disconnected. This risk more particularly occurs when there is an excessive clearance between the hook and the fork. In the presence of the mismatching J2 (FIG. 4), the vibrations of the engine 6 and the miscellaneous, relative movements can consequently disconnect the hooks, thereby casting into doubt once again the integrity of the locking function which they fulfil.
The invention specifically relates to an aircraft propulsion system, such as a jet engine, whose original design makes it possible to eliminate all the disadvantages of the prior art and which have been described hereinbefore and more particularly the appearance of a radial clearance between the lower part of the cowls and the air intake structure when the aircraft is flying, so as to avoid accelerated erosion of the leading edge of the cowls and a risk of the latter being accidentally torn away due to the disconnection of the hooked locks.
According to the invention, this result is achieved by means of an aircraft propulsion system, comprising an engine, a pod placed round the engine in accordance with a common longitudinal axis, and a strut supporting the engine, the pod including two cowls having a C-shaped cross-section, articulated to the strut and which can be connected to one another, in the closed position, by locking means, characterized in that front guide means are interposed between the cowls and the part carried by the engine or by an air intake structure of the pod, in the vicinity of the locking means and a front edge of the cowls, so as to oppose a relative displacement between the cowls and the engine, axially and radially with respect to said longitudinal axis, when the cowls are in the closed position.
In a preferred embodiment of the invention, the front guide means comprise at least one front thrust bearing integral with the part carried by the engine or by the air intake structure and a front guide integral with each of the cowls. Each of the front guides then automatically cooperates with the front thrust bearing when the cowls are in the closed position.
In this case, as a function of the particular case, the front guide means can comprise either a single, front thrust bearing, or two front thrust bearings, each of the front guides then cooperating with one of said thrust bearings when the cowls are in the closed position.
In the preferred embodiment of the invention, the front thrust bearing is advantageously fixed to a circular collar and to a radial flange materializing the rear end of the air intake structure of the pod.
An adjustment of the position of the front thrust bearing can then be interposing radial and axial adjusting shims respectively between the front thrust bearing and the circular collar and between the front thrust bearing and the radial flange.
Advantageously, when the locking means are not locked, the front guide means maintain the cowls in a natural position, substantially differing from the closed position, in which the adjacent edges of the cowls are spaced from one another in a visible manner. This arrangement makes it very easy for personnel carrying out maintenance to visually check that the locking means are indeed locked.
The natural position of the cowls permitting said visual check can be defined by a contact by gravity between each of the front guides and the front thrust bearing, so that a passage into the closed position requires the application of a circumferential force between the cowls by the locking means.
In the preferred embodiment of the invention, rear guide means are also interposed between the cowls and a second part carried by the engine or by a rear part of the pod, in the vicinity of the locking means of a rear edge of the cowls, so as to oppose a relative displacement between the cowls and the engine, radially with respect to the longitudinal axis of the engine, when the cowls are in the closed position.
In this case, the rear guide means advantageously comprise a rear thrust bearing integral with the second part carried by the engine or the rear part of the pod, and a rear guide integral with each of the cowls, each rear guide automatically cooperating with the rear thrust bearing when the locking means are in the closed position.
The rear thrust bearing can be fixed to a second circular collar and to a second flange, materializing a front end of the rear part of the pod.
As a variant, the rear thrust bearing can also be fixed directly to the engine.